Effects of goldfish (Carassius auratus) population size and body condition on the transmission of Gyrodactylus kobayashii (Monogenea)

Abstract

Field surveys indicate that host population size, rather than density, is the most important determinant of monogenean infection dynamics. To verify this prediction, epidemic parameters were monitored for 70 days at five host population sizes held at constant density using a goldfish - Gyrodactylus kobayashii laboratory model. During the first 20 days, the rate of increase of prevalence and mean abundance was faster in small host populations. Total mean prevalence and total mean abundance throughout the experiment were not significantly affected by host population sizes. Higher transmission rates were detected in larger host populations. However, there were no significant differences in effective contact rates among the five host populations on each sampling day during the first 20 days, implying that contact rates may be saturated at a sufficiently high host density. These results demonstrate that the epidemic occurs more quickly in smaller host populations at the beginning of the experiment. However, the epidemic is independent of the host population size due to the similar effective contact rates in the five population sizes. Significant negative influence of the initial body condition (Kn) of uninfected goldfish on total mean abundance of parasites suggests that susceptibility of hosts is also a determinant of parasite transmission.

Morphology is not a reliable taxonomic tool for the genus Lernaea: molecular data and experimental infection reveal that L. cyprinacea and L. cruciata are conspecific

“…The two experimental populations were kept in two separate, aerated tanks (30% water exchanged fortnightly) for 30 days: goldfish ( n = 125) in a 500 litre tank, and mosquitofish ( n =73) in a 30 litre tank. To remove all ectoparasites, all experimental fish were treated with three consecutive baths in 1:10,000 formalin solution for 12 h at 48 h intervals [32]. Treated fish were then examined under a dissection microscope to ensure that they are free of Lernaea parasites.…”

Transmission dynamics of ectoparasitic gyrodactylids (Platyhelminthes, Monogenea): An integrative review

“…Two gyrodactylid hosts show both responses results; in guppies, P. reticulata there is a positive relation between condition of an initial ‘source’ fish (a fish with high relative condition index, K n ) and major epidemic variables (i.e., parasite incidence, peak parasite load and the degree of parasite aggregation), resulting in parasites either aggregated on ‘source’ hosts of high condition or transferred to hosts of high condition (Tadiri et al ., 2013). In goldfish, C. auratus , there is a negative influence of initial body condition of uninfected fish on total abundance of parasites (Zhou et al ., 2017). Computer models propose that larger fish are individuals with higher relative condition that support heavier parasite loads because larger fish can offer more living space for parasites (van Oosterhout et al ., 2008), however, further research into host body condition and fish size on mapping parasite transmission is needed.…”

“…The most important route of transmission in gyrodactylids is direct contact between infected and uninfected fish, either between live hosts or from a dead to a live host (Scott and Anderson, 1984). Then, according to the simple transmission function d I /d t = βSI /( S + I ), where β is the transmission coefficient (Getz and Pickering, 1983; Anderson and May, 1992; Lloyd-Smith et al ., 2005 a , 2005 b ), S , the number of susceptible hosts, and I as the number of infected hosts (Smith et al ., 2009; McCallum et al ., 2017), the probability of transmission in the genus Gyrodactylus could be at a rate βSI (frequency-dependent transmission) rather than βSI /N (density-dependent transmission) (Heggberget and Johnsen, 1982; Johnsen and Jensen, 1986, 1992; Johnson et al ., 2011; Zhou et al ., 2017). Still, because pathogen transmission often occurs through more than one route, each of which may have a different functional relationship with population density (Ryder et al ., 2007), it is likely that Gyrodactylus transmission combines frequency- and density-dependent dynamics.…”

Antiparasitic Efficacy of Herbal Extracts and Active Compound Against Gyrodactylus kobayashii in Carassius auratus

“…And then, G. kobayashii-infected goldfish maintained in the laboratory were mix-cultured with these ectoparasite-free goldfish for about 10 days at a ratio of 1:4 to obtain more infected goldfish. The goldfish-G. kobayashii model has been established and maintained in the laboratory referring to the methods reported in previous studies (24,25).…”